Brain slice experiments are a mainstay of modern neuroscience: They allow scientists to probe the molecular details of the brain while keeping brain architecture intact. Scientists usually bathe these slices in artificial cerebrospinal fluid (CSF) instead of CSF obtained from humans. This typically works well, but neurons in brain slices are often quieter than those in intact brains. However, when Bjorefeldt et al. replaced articial CSF with real human CSF, they observed a neuronal activity boost. Pyramidal neurons exhibited lower action potential thresholds and their excitability increased. The authors hypothesized that endogenous neuromodulating substances in the human CSF increased the excitability of the nerve cells.